1. Field of the Invention
The present invention relates generally to methods for making optical fiber preforms and optical fibers and, more specifically, to methods of making optical fiber preforms containing gaseous voids and microstructured optical fibers.
2. Technical Background
Optical fibers formed of glass materials have been in commercial use for more than two decades. Although such optical fibers have represented a quantum leap forward in the field of telecommunications, work on alternative optical fiber designs continues. One promising type of alternative optical fiber is the microstructured optical fiber, which includes holes, also commonly referred to as voids, running longitudinally along the fiber axis. The holes generally contain air or an inert gas, but may also contain other materials. The majority of microstructured fibers have a plurality of holes located around the core, wherein the holes extend along the entire length of the optical fiber. These cladding holes are also most typically arranged in a regular, periodic formation around the core of the optical fiber. In other words, if cross sections of the optical fiber are taken along the length of the optical fiber, the same individual holes can be found in essentially the same periodic hole structure relative to one another.
Microstructured optical fibers have previously been manufactured by the so-called “stack-and-draw” method, wherein an array of silica rods and/or tubes are stacked in a close-packed arrangement to form a preform, that can be drawn into fiber using a conventional tower setup. There are several disadvantages to the stack and draw method. The awkwardness of assembling hundreds of very thin canes (defined by rods or tubes), as well as the possible presence of interstitial cavities when stacking and drawing cylindrical canes, may affect dramatically the fiber attenuation by introducing soluble and particulate impurities, undesired interfaces and inducing a reshaping or deformation of the starting holes. Moreover, the relatively low productivity and high cost make this method not much suitable for industrial production.